1. Field of the Invention
The present invention is related to centrifugal blood pumps.
2. Description of the Prior Art
Centrifugal pumps have been used for many years to pump a wide variety of different fluid materials. In general, a centrifugal pump includes a pump housing enclosing a pumping chamber therein, an inlet aligned with a rotational axis of the pump, an outlet adjacent to the periphery of the pumping chamber, a rotator mounted within the pumping chamber for rotation about the axis, and a drive source communicating with the rotator. The rotator and drive source have several possible configurations. In one configuration, the rotator is mounted on a drive shaft which extends outside the pumping chamber to a rotational drive source. In another configuration, the pump housing encloses two chambers, one containing a magnetic rotor and the other containing the pumping chamber and rotator. The rotator and rotor are connected by a drive shaft. Seals are used to isolate the two chambers. A magnetic drive source communicates with the rotor to rotate the rotator within the pumping chamber. In still another configuration, the rotator is suspended within the pumping chamber by a magnetic means formed within the pump housing. Examples of these centrifugal pumps are shown in the following U.S. Patents: Kletschka et al U.S. Pat. No. 3,864,055; Rafferty et al U.S. Pat. No. 3,647,324; and Olsen et al U.S. Pat. No. 4,688,998.
In recent years, centrifugal pumps have been used extensively for pumping blood during open heart surgery. The pumping of blood requires great care to avoid any damage to the red corpuscles, or any of the other constituents of blood. Any practical blood pump useful as part of heart/lung bypass equipment during open heart surgery must deliver the requisite flow volumes under pressure, without damaging the blood being pumped.
In a prior art centrifugal pump, and in particular in a centrifugal pump for pumping liquids such as blood, a fluid tight seal between the drive shaft and the housing is an important factor in the performance of the pump. Friction at the seal produces heat which, if not dissipated, can damage both the components of the pump and the blood being pumped. Also, the rotation of the rotator can lead to generation of an air bubble surrounding the shaft. This air bubble tends to seek the smallest shaft diameter, which typically is adjacent the drive shaft seal. In some of the prior art pumps, the area adjacent the drive shaft seal has also been a relatively stagnant or low flow area in terms of fluid flow within the pumping chamber. The air bubble tends to insulate the seal from the flow of the fluid within the pumping chamber, thus decreasing the dissipation of heat generated by friction at the seal surface.
It is often the case that blood pumps are used only once. After a single use, the portions of the pump which contact the blood must either be disposed of or its constituent parts must be sterilized. A centrifugal blood pump comprising a minimal number of parts is desirable to reduce costs and improve reliability.